Molecular cloning and expression analysis of a mouse UDP-GlcNAc : Gal(beta1-4)Glc(NAc)-R beta 1,3-N-acetylglucosaminyltransferase homologous to Drosophila melanogaster Brainiac and the beta 1,3-galactosyltransferase family

We have isolated a murine cDNA coding for a beta1,3-N-acetylglucosaminyltra nsferase enzyme (beta 3GnT). This enzyme is similar in sequence to Drosophi la melanogaster Brainiac and to the murine and human beta1,3-galactosyltran sferase family of proteins. The mouse beta 3GnT protein is 397 amino acids in length and contains 7 cysteine residues that are conserved in the human orthologue. beta 3GnT is a type II membrane protein localized to the Golgi apparatus. Enzyme assays with recombinant mouse beta 3GnT reveal that it ha s a preference for acceptors with Gal(beta1-4)Glc(NAc) at the non-reducing termini. Proton NMR analysis of product showed incorporation of GlcNAc in b eta1,3 linkage to the terminal Gal of Gal(beta1-4)Glc(beta1-O-benzyl). Nort hern blot analysis revealed the presence of a single 3.0 kb transcript in a ll adult mouse and human organs tested, with highest levels in the kidney, liver, heart and placenta. The beta 3GnT gene is also expressed in a number of tumor cell lines. The human orthologue of beta 3GnT is located on chrom osome 2pl5.